Abstract

To get a transparent polyimide and investigate the isomeric effect of trans and cis configuration, two novel dianhydrides, trans- and cis-1,4-bis(3,4-dicarboxyphenoxy)cyclohexane dianhydrides were synthesized (trans-2 and cis-2), and polycondensations of the dianhydrides with different aromatic diamines containing trifluoromethyl group or meta-substituent were carried out by two-step procedure. The resulting polyimides had glass transition temperature (Tg) in the range of 203–262 °C, and exhibited good mechanical properties with tensile strengths of 53–102 MPa, tensile moduli of 2.1–3.3 GPa, and elongations at break of 1.9–16.5 %. All semi-aromatic polyimide films showed high optical transparency in the visible region along with the cut-off wavelength of 369–375 nm due to the introduction of cyclohexane moiety into the main chain. Furthermore, compared with cis-2-based polyimides, the polyimides derived from trans-2 had higher Tg, better chemical solvent resistance and mechanical properties. It could be attributed to the relatively denser polymer chain packing in trans-2 based polyimides, which was confirmed by wide-angle X-ray diffraction.

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Acknowledgments

This work was financially supported by Zhejiang Provincial Natural Science Foundation of China (Grant No. LQ12B04001), and Natural Science Foundation of Ningbo City, China (No. 2012A610088). The authors also express their thanks to the Program for Ningbo Innovative Research Team (Grant No.2009B21008), Ningbo Key Lab of Polymer Materials (Grant No. 2010A22001) and Guangdong Province and Chinese Academy of Science Comprehensive Strategic Cooperation Project (Grant No. 2011B090300094) for their financial support of this work.